Carrier-amplitude control in radio systems



March 26, 1929. w, H, T, HOLD N 1,705,490

CARRIER AMPLITUDE CONTROL IN RADIO SYSTEMS Filed Feb. 17, 1926 11V VENTOR ATTORNEY Patented Mar. 26, 1929.

UNITED STATES.

PATENT OFFICE.

wn'imm n. 'r. normmr, or snooxmm, new. onmhssrenoa TO AMERICAN, TELE-PHONE AND TELEGRAPH COMPANY, .65 coaroaarron or NEW YORK. I

CARRIER-AMPLITUDE CONTBOLIN RADIO SYSTEMS.

Application filed February 17, 1926. SerialNo. 88,922.

This invention relates to wave control systems, and more particularly toarrangements for controlling the amplitude of a. carrier wave inaccordance with the ampll able noise in a radio receiver when suchcarrier frequency is detected by the radio receiver modulated by lowfrequency signal- 1 ing oscillations of low or of negligible amphtude.During the transmission of a carrier frequency modulated by lowfrequency signals, when the amplitude of the low frequency signalsdecreases the noise 1s clearly heard in'the loud speaker at the radloreceiver. The noise is objectionable and should be minimized.Furthermore, when the low frequency signals have a high level, the ratiobetween the modulation of these low frequency signals and the noise isnot sufficient to be noticeable at the radio receiver.

In this invention there is disclosed a wave control system in which theamount of carrier radiated depends upon the level of the v low frequencysignals supplied to the system to a considerably greater extent than isordinarily the case.

It is the object of the invention to vary the amplitude of a carrierwave in accordance with variations in the amplitude of low frequencysignals. In other words, it is an object of the invention to increasethe amplitude of a carrier wave as the level of low frequency signalsincreases, and vice versa.

Other objectsand features of the invention will be better understoodfromthe detailed description hereinafter following when read inconnection with the accompanying drawing showing one embodiment of theinvention suitable for controlling a carrier wave in accordance with lowfrequency .signals.

Referring to the drawing, the reference character L represents leadsconnected to a low frequency signaling source which may be, for example,a voice frequency signaling source. The leads L are also connected to anamplifier A for amplifying these signals.

This amplifierv may be of any type well (fully in the descriptionhereinafter followknown in the art, preferably avacuum tube amplifier,An oscillator is represented by the reference character 0, whlchoscillator supplies the carrier frequency, to be employed in the system.This oscillator may be of any Well-known type, preferably a vacuum tubeoscillator suitable for setting up oscillations of constant frequencyand amplitude. Two three-electrode vacuum tubes V and V each having ananode, a cathode, and a grid are employed for controlling the amplitudeof the carrier in ac- .cordance with the amplitude of the low fre quencysignals, as. will be explained more ing.'

The output of the amplifier A is connected to the grid and cathode ofthe vacuum tube V through a condenser 11 and resistance 12. The outputof the oscillator O is connected to the input circuit of the vacuum tubeV current flowing in the circuit including the resistance 13, thecondenser 14, the resistance 15, battery 16, and ground, the resistance15 and battery 16 being directly connected between the grid andcathodeof the vacuum tube V The anodes of the vacuum tubes V and V aresupplied with direct current potential from batteries 17 and 18 throughthe choke coils 19 and 20, respectively. The anode of'the vacuum tube Vis directly connected to the grid of the vacuum tube V through acondenser 21 which prevents the potential of the battery 17 from beingapplied to'the' grid of the vacuum tube V The output of the vacuum tubeV is connected through a condenser 22 with a filter F which may be ofany wellknown type, preferably of the type disclosed in the patent to G.A. Campbell,-dated May 22, 1917, No. 1,227,113, freely transmitting thecarrier frequency and substantially suppressing all other frequencies.The output of the filter F is connected with the output circuit Lthrough a transformer T. 1 The condenser 11 and the resistance 12 are sorelated to the amplified low frequency signaling oscillations that thepotential existing between the grid and cathode of the vacuum tube Vvaries in accordance with the variations in the amplitude of the lowfrequency signals. The anode and cathode of the vacuum tube V are inparallel relationship' with the resistance 15, so that any variation inthe plate-filament impedance of the vacuum tube V causes a corresponding variation in the magnitude ofthe h gh frequency potential dropacross the resistance 15. When the level of the low frequency signalsapplied to the vacuum tube V is low, the otential between the grid andcathode of t e vacuum tube V, will also be low. The plate-filamentimpedance of the vacuum tube V will be low, and therefore,-

I tube V,, thereby increasing the plate-filament impedance of the vacuumtube V and effecting a corresponding increase in the potential dropacross the resistance 15. "Therefore, the amplitude of the carrier wavewill be considerably increased. Thus it will benoted that the vacuumtubes V and V together form an arrangement which is employed forcontrolling the amplitudeof the carrier wave in accordance with thelevel of the low frequency signals.

The anode and cathode of the vacuum tube V are connected to the input ofthe filter F througha condenser 22 which prevents the potential of thebattery 18 from being applied to the filter F. The filter F freelytransmits the carrier frequency 'of the oscillator O and substantiallysuppresses all other frequencies, which other frequencies may includethe harmonics of the low fre quency signals and the carrier frequency.The output of the filter F- is connected to the output circuit L througha transformer T.

.While the arrangements of the invention have been shown with to asystem for the control of a carrier fre quency, it is to be understoodthat the invention may be embodied in other systems and in other andwidely varied organizations without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:

1. In combination, a-source of low frequency signals of varyingamplitude, a carrier frequency oscillator, means for controlling theamplitude of the carrier frequency of the oscillator in accordance withthe amplitude of the low frequency signals, said means comprising twothree-electrode vac-,

uum tubes each having an input circuit and an output circuit, the sourceof low frequency signals being connected to the input circuit of one ofthe vacuum tubes and the carrier frequency oscillator being connected tothe input circuit of the other of the vac- .uum tubes, the outputcircuit of the vacuum tube to which the source of low frequencyarticular reference signals is connected being in parallel relationshipwith the input circuit of' the vacuum tube to which the carrierfrequency oscillator is connected, the output circuit of the lattervacuum tube receiving a carrier frequency variedin amplitude inaccordance with the amplitude variations of the low frequency signals.

2. A system for controlling the amplitude of a carrier frequency inaccordance with the amplitude of low frequency signals, which comprisesa source of low frequency signals of varying amplitude, a carrierfrequency oscilator, and a pair of three-elec trode vacuum tubes placedin tandem with respect to the source of low frequency signals so thatthe plate-filament circuit of the first vacuum tube is in parallelrelationship with the grid-filament circuit of the second vacuum tube,the low frequency signals being impressed on the grid and filament ofthe first vacuum tube and the carrier frequency being impressed on thegrid and filament of, the second vacuum tube, variations in theyamplitude ofthe low frequency signals causing corresponding variationsin the amplitude of the carrier frequency.

3. A system for controlling the ampli tude of a carrier frequency inaccordance with low frequency signals of varying amplitude, comprising asource of low frequency signals of varying amplitude, a carrierfrequency oscillator, and two three-electrode vacuum tubes placed intandem with respect to the source of low frequency signals so that theplateand filament of the first vacuum tube are in parallel relationshipwiththe grid and filament of the second vacuum tube, the source of lowfrequency signals being connected to the grid and fila ment of the firstvacuum tube and the car rier frequency oscillator being connected to thegrid and filament of the second vacuum tube,and .a filter connected tothe plate and filament of the second vacuum tube freely transmitting thecarrier .frequency controlled .as to its amplitude and substantiallysup-- pressing all other frequencies.

4-. In a system for controlling the amplitude of a carrier frequencyWave in accordance with variations in the amplitude of low frequencysignals, in combination, a source of low frequency signals, a carrierfrequency generator, two three-electrode vacuum tubes each having aninput circuit and an output circuit, the source of low frequency si nalsbeing connected to the input circuit 0 one of the three-electrode vacuumtubes and the carrler frequency generator being connected to the inputcircuit of the other of the threeelectrode vacuum tubes, saidthree-electrode vacuum tubes being so related that variations in thepotential in the input circuit of the three-electrode vacuum tube towhich thesource of low frequency signals is con nected causecorresponding variations in the current in the output circuit of thethree-- electrode tube to which the source of low frequency signals isconnected and corresponding variations in the current in the outputcircuit of the three-electrode tube to which the carrier frequencygenerator is connected. I

5. In afisystem for controlling the amplitude of a.carrier frequencywave in accord-v ance with low frequency signals of varying amplitude,in ombinatlon, a source of low cathode of the other of thethree-el'ectrodel vacuum tubes, said three-electrode vacuum tubes beingso related that variations in the potential between the grid and cathodeof the three-electrode vacuum tube to which the source of low frequencysignals is connected cause corresponding variations in the amplitude ofthe current flowing between the anode and cathode of the three-electrodevacuum tube to whichthe carrier frequency generator is connected.

6. In combination, a source of low freuency signals of varyingamplitude, a high If two three-element vacuum tubes each having a plate,a filament and a grid, the source of low frequency signals beingconnected to the grid andfilament of one of the three-electrode vacuumtubes so as to effect changes in the potential of the grid with respectto the filament of that tube at a rate corresponding to the variationsin the amplitude of the low frequency signals, the high frequencygenerator being connected to the grid and filament of the'other of thethree-electrode vacuum tubes, said three-element vacuum tubes being soconnected that chan es in the plate-filament impedance of the tres-electrode vacuum tube to which the source of low frequency signalsis connected efiect corresponding changes in the potential of the gridwith respect to the filament of the three-electrode vacuum tube to whichthe high frequency generator is connected.

7. In combination, a source of low frequency signals of varyingamplitude, two three-element vacuum tubes each having a plate, afilament and a grid, the source of low frequency signals bein connectedto the grid and filament of the rst of the threeelement vacuum tubes,said three-element vacuum tubes being so related to the source of lowfrequency signals that variations in the amplitude of the low frequencysignals cause corresponding variations in the potential between the gridand filament of the second of the three-element vacuum tubes, and anoscillator of constant fre' uency connected to the grid and filament othe second of the three-element vacuum tubes, the amplitude of the waveproduced by said oscillator varying with variations in the amplitude ofthe low frequency signals.

8. In a system for controlling the amplitude of a carrier wave inaccordance with voice frequencies of varying amplitude, in combination,an oscillator setting up a currentconstant in amplitude and frequency, athree-element vacuum tube having-a late, a filament and-a grid, saidoscillator eing connected. to the grid and filament of saidthree-electrode vacuum tube, a source of voice frequencies of varyingamplitude, and means for varying the amplitude of the current set up bysaid'oscillator' in accordance with the amplitude of the voice freuencies, said means comprising another t ree-ele ment vacuum tube havinga plate, a filament vand a grid, the grid and filament of said latterthree-electrode vacuum tube being connected to the source of voicefrequencies, the plate and filament of said latter threeelement vacuumtube being in parallel relationship with the grid and filament of the

